Wing in ground effect vehicle with endplates

ABSTRACT

A Wing In Ground Effect Vehicle has a pair of supercavitating endplates ( 17 ) which extend below the fuselage ( 2 ) such that they can be immersed in water during flight thereover. The endplates have a nose ( 28 ) defining a leading edge ( 20 ) and adapted to generate a supercavity. The endplates ( 17 ) typically pivot about a pivot axis P to provide a stabilising weathercock-type effect.

This application is a continuation-in-part of application Ser. No.09/573,385, filed May 18, 2000 now abandoned.

FIELD OF THE INVENTION

The present invention relates to Wing In Ground Effect Vehicles (WIGs)and more particularly to WIGs with endplates that operate over water.

BACKGROUND OF THE INVENTION

A significant part of the drag of transport aircraft is made up ofinduced drag. Flying in ground effect close to the ground or water canreduce this drag. Numerous WIGs have been developed and flown.

Several large WIG designs have been proposed but never built. These aresummarised in two reports, “Air Cushion Craft Development (FirstRevision)” (DTNSRDC Report 80/012 (4727 revised) January 1980) by PeterJ. Mantle (hereinafter referred to as the Mantle Report), and “WingshipInvestigation” (Advanced Research Projects Agency, Sept. 30, 1994)(hereinafter referred to as the ARPA Report).

Because the height of land varies so much it is normal to fly WIGs overwater. All existing WIGs fly entirely above the water at the height ofthe highest wave expected to be encountered plus a margin of safety.This is because of the extremely high wave impact forces that would beincurred at cruise speed. The ARPA Report concluded that designing basicstructure and mission loads to tolerate impact with large waves isprobably impracticable.

The ARPA Report also concludes that the induced drag increases and thePower Augmented Ram (PAR) lift decreases with the height of theendplates above the water. PAR directs the jet from engines locatedforward of the wing under the wing to provide added lift at slowerspeeds. Because of this there is an advantage for WIG endplates topenetrate the waves so that there is no gap at the wave trough betweenthe bottom of the endplate and the water. The existing prior art has nottaken advantage of the above as it has been assumed to be impossible todesign wave piercing endplates that would (i) have a low enough drag inthe water and (ii) be stable at expected angles of yaw at design cruisespeed.

As a result, the endplates of existing WIGs usually resemble slenderhull shapes similar to high speed racing catamarans, some of whichinclude steps to reduce water friction on take-off. Because thesedesigns are still relatively thick they would incur severe wave impactpressures at cruise speed as well as high drag. Consequently, theseendplates are designed to be no lower than the lowest part of thefuselage of the WIG. As a result there is always an air gap greater thanthe wave height between the wing tip or endplate and the trough of eachwave. This restricts their ability to reduce the induced drag. Typicallift/drag ratios of Russian craft are around 18:1 and the ARPA Reportstudy was unable to significantly improve on this figure even for a verylarge craft of 5,000 tonnes (after making changes required to achievethe longer range set by the study). As these lift/drag ratios are nobetter than those achieved by aircraft it is understandable why WIGshave never been commercialised.

The WIG configuration that has reached the highest level of technicalmaturity is the Russian “ekranoplan.” This is described further in theARPA Report. A typical example of the “ekranoplan” configuration isembodied in the Russian Orlyonok, depicted in FIGS. 1( a) to 1(c). Inthis prior art WIG, turbofan engines 1 are located on either side of thefuselage 2. These engines 1 are used for underwing blowing PAR toincrease the lift of the wing 3 during take-off and landing therebyreducing take-off and landing speeds. The turbo prop engine 4 providesefficient thrust for cruise. The horizontal stabiliser 5 controls thepitching moment. A hydro ski 6 (shown in its lowered position) can belowered to reduce hull impact pressures on landing. The endplates 7 helpcontain the pressure under the wing 3 to provide increased PAR liftduring take-off and landing. Because the endplates 7 do not extend belowthe lowest part of the fuselage 2 the effective air gap 8 between theendplates 7 and the water 9 is no less than the gap 10 between thelowest part of the fuselage 2 and the water 9. The ability of theendplates 7 to reduce the induced drag is therefore limited.

FIGS. 2( a) and 2(b) illustrates the side and plan views of the thickprior art endplates 7 of the Orlyonok WIG. On take-off and landing theseendplates 7 are designed to plane on the water surface 9 while thefuselage 2 is still supported by the water 9. Steps 12 in the bottomsurface of the endplates help this planing action. The sides 13 arecontoured to reduce air drag.

The U.S. Navy used thinner endplates with their PAR WIG modelexperiments disclosed at page 411 of the Mantle Report. These endplateswere designed to pierce the waves but were unstable at cruise speed witha moderate angle of yaw. Even if these endplates did not fail, theirrelatively thick leading edge and forebody would make the drag of theseendplates intolerably high when piercing waves at high speed.

In a report entitled “Force and Spray Characteristics of Wing EndplatesPenetrating the Water Surface” (General Dynamics/Convair ReportGD/C-64-100, April 1964) by W H Barkley (hereinafter referred to as theBarkley Report), four thin endplates with various nose shapes and sideconfigurations are disclosed. Models of these configurations were testedin a towing tank and lift, drag and side forces were measured. Whenthese endplate designs are scaled up to full-scale sizes, the dragforces on the Barkley design are prohibitively high. The raked bottom ofthree of the Barkley Report designs tested would allow a large air gapand thus cause an increase in induced drag.

FIGS. 3( a), 3(b) and 3(c) provide side elevation, plan and enlargedfragmentary plan views of the thin prior art endplates 14 as disclosedin the Barkley Report and similar to that used on the model in the USNavy experiments referred to in the Mantle Report. As shown in FIG. 3(c) these thin prior art endplates 14 had rounded noses 15 and parallelsides 16. The Mantle report, page 414, concluded that this type ofparallel sided, round nosed endplate 14 would fail structurally atcruise speeds.

FIGS. 4( a) to 4(c) depict front, plan and side views of GeneralDynamics/Convair's test model No. 4 described in the Barkley Report.These endplates 55 have the advantage of a small amount of side forcewhen exposed to moderate amounts of yaw alone (Run No. 5). They dohowever experience high side forces when certain angles of yaw and rollare combined (Run No. 6). These endplates 55 therefore need to be quitethick to resist the side force resulting in a high drag.

The endplate model No. 4 tested in the Barkley Report had the followingdimensions: thickness—1″ (25 mm), working depth—4″ (100 mm), chordlength—2′ (610 mm). Scaled up to a depth of 144″ (3.7 m) the dimensionswould be: thickness-36″ (914 mm), depth—144″ (3.7 m) and chordlength—72′ (22 m). The strength of such an endplate would likely besufficient but the large thickness would provide excessive drag.

In papers by J. W. Moore, including “Conceptual Design Study of PowerAugmented Ram Wing-In-Ground Effect Aircraft” (AIAA Paper 78-1466, LosAngeles, Calif., August, 1978) (herein after referred to as the MooreReport), endplates as depicted in FIGS. 5( a) to 5(c) and based on modelNo. 4 of the Barkley Report were proposed. Because of their high drag,these endplates 57 were designed to operate above the water most of thetime except for impact with every 1/1000 wave crest to a depth of 0.63′(192 mm) and 1.4′ (427 mm) for sea states 3 and 4 respectively. The dragforce of each endplate 57 was calculated as 687,000 lbs (3.06 MN) and1,148,000 lbs (5.11 MN) at an immersion depth of 1.4′ (427 mm) and yawangles of 0 degrees and 10 degrees respectively. For the two endplates57 the total drag would be 1,374,000 lbs (6.112 MN) at 0 yaw and2,296,000-lbs (10.21 MN) at 10 degrees yaw, equivalent to 88% and 147%of the gross weight of the entire WIG (for an immersion depth of only1.4′ (427 mm)). This extremely high drag is caused by the thick wedgenose 58 chosen “to assure non-attached flow along the endplate length”when impacting every 1/1000 wave crest. The endplates 57 are notdesigned for and would be completely impracticable for continuousimmersion to the depth of the wave trough, as the drag would besufficient to down the WIG. In addition Moore concluded that the highside force in yaw would create structural failure of the endplate 57 atan immersion depth of 4.3′ (1300 mm) and a speed of 265 knots (136 m/s)in a sea state 4.

The prior art endplates discussed above generally have very high dragcharacteristics and lack of stability if immersed in water.

In two further reports, “On the Minimum Induced Drag of Ground EffectWings,” (The Aeronautical Quarterly, Royal Aeronautical Society, London,UK, August 1970) by P. R. Ashill (hereinafter referred to as the AshillReport) and “Wind-Tunnel Investigation of Single and TandemLow-Aspect-Ratio Wings In Ground Effect” (Lockheed Calif., March 1964)(hereinafter referred to as the Lockheed Report), it was shown that theaddition of vertical plates at each end of the wing can be used toreduce or eliminate the induced drag.

Ashill concludes that the induced drag→0 as l/b→h/b (where l=distancefrom the bottom edge of the wing at the ¼ chord point to the bottom ofthe endplate, h=distance between from the bottom edge of the wing at the¼ chord point to the ground and b=span of wing). This is confirmed bythe following extrapolation of the results found in FIGS. 17 and 18 ofthe Lockheed Report, reproduced here as Tables 1 and 2 wherein:

C_(l)=lift coefficient, L/D=lift/drag ratio, AR=aspect ratio of thewing, h=distance between bottom of the endplate and the ground; S=areaof the wing and O.G.E.=2-dimensional test Out Of Ground Effect.

TABLE 1 Flat Endplates, AR = 4, Endplate depth = 0.15 chord InducedDrag/ C_(l)/(L/D) h/√{square root over (S)} Total Drag Induced Drag√{square root over (()}h/√{square root over (S)}) 0.5/50 O.G.E. 0.01 0.0— 0.5/38 0.01 0.01316 0.00316 0.0316 0.5/35 0.02 0.01429 0.00429 0.03030.5/30 0.04 0.01667 0.00667 0.0333

TABLE 2 Contoured Endplates, AR = 4, Endplate depth = 0.015 chordInduced Drag/ C₁/(L/D) h/√{square root over (S)} Total Drag Induced Drag√{square root over (()}h/√{square root over (S)}) 0.5/56 O.G.E. 0.008930.0 — 0.5/40 0.01 0.0125 0.00357 0.0357 0.5/36 0.02 0.0139 0.004970.0355 0.5/31 0.04 0.016 0.007 0.035 

These figures show that, for small values of h/√{square root over (S)},the induced drag/(h/√{square root over (S))}≈constant. Thus the InducedDrag approaches zero as h approaches zero.

The application of this concept can effectively raise the elevation ofthe basic structure so as to avoid its impact with waves. Thus ifendplates could be designed with adequate structural strength and lowenough drag to operate immersed in the water, a WIG with attractiveperformance could be achieved.

OBJECT OF THE INVENTION

It is an object of the invention to provide an improved wing in groundeffect vehicle with endplates capable of operating immersed in water.

SUMMARY OF THE INVENTION

In a broad form the present invention provides a wing in ground effectvehicle having a fuselage and wing structure with opposing wing tipportions and a pair of supercavitating endplates each extendingdownwardly from a respective said wing tip portion to below saidfuselage and wing structure for immersion in water during flightthereover, each said endplate having:

a proximal root,

a distal tip,

a forward portion including a nose defining a leading edge of saidendplate and terminating in a nose lateral edge on each lateral side ofsaid endplate, said nose being adapted to generate a cavity extendingrearwardly from each said nose lateral edge between the respective saidlateral side of said endplate and water passing over said endplate, inuse, at a zero yaw condition at speeds up to and including a designcruise speed with said endplate immersed in water to a design immersiondepth, said cavities forming a supercavity at said design cruise speed,and

an aft portion terminating in a trailing edge,

wherein at least part of said forward portion of each said endplate islaterally fixed with respect to the respective said wing tip portion andsaid trailing edge of each said endplate is laterally displaceable, withrespect to the respective said wing tip portion, by water flowing oversaid endplate in use.

In another broad form the present invention provides a wing in groundeffect vehicle having a fuselage and wing structure with opposing wingtip portions and a pair of supercavitating endplates each extendingdownwardly from a respective said wing tip portion to below saidfuselage and wing structure for immersion in water during flightthereover, each said endplate having:

a proximal root,

a distal tip,

a forward portion including a nose defining a leading edge of saidendplate and terminating in a nose lateral edge on each lateral side ofsaid endplate, said nose being adapted to generate a cavity extendingrearwardly from each said nose lateral edge between the respective saidlateral side of said endplate and water passing over said endplate, inuse, at a zero yaw condition at speeds up to and including a designcruise speed with said endplate immersed in water to a design immersiondepth, said cavities forming a supercavity at said design cruise speed,and

an aft portion terminating in a trailing edge,

wherein said nose of each said endplate is substantially flat and liesin a plane substantially perpendicular to the chord-wise direction ofsaid endplate.

Preferably, each said endplate is pivotably mounted about a pivot axisextending in a span-wise direction of said endplate, said forwardportion of each said end plate being laterally fixed at said pivot axis.

The wing in ground effect vehicle may further comprise means foractively controlling rotation of said endplates about the respectivesaid pivot axes.

In an alternate form, said forward portion of each said endplate isfixed and said aft portion of each said endplate is pivotally mountedabout a pivot axis extending in a span-wise direction of said endplate.

Preferably, said pivot axis of each said endplate is located forward ofthe hydrodynamic centre of pressure of said endplate at said designcruise speed with said endplate immersed in water to said designimmersion depth.

Preferably, said pivot axis of each said endplate is located less than0.25 times the chord length of said endplate aft of said leading edge ata span-wise position midway between said endplate root and tip.

In another alternate form, said forward portion of each said endplate isfixed and said aft portion of each said endplate is laterally flexibleand is mounted to the respective said forward portion.

Preferably, said aft portion of each said endplate extends forward ofthe hydrodynamic centre of pressure of said endplate at said designcruise speed with said endplate immersed in water to said designimmersion depth.

Preferably, said aft portion of each said endplate has a chord length ofat least 0.75 times the chord length of said endplate at a span-wiseposition midway between said endplate root and tip.

In another broad form the present invention provides a wing in groundeffect vehicle having a fuselage and wing structure with opposing wingtip portions and a pair of supercavitating endplates each extendingdownwardly from a respective said wing tip portion to below saidfuselage and wing structure for immersion in water during flightthereover each said endplate having:

a proximal root,

a distal tip,

a forward portion including a nose defining a leading edge and adaptedto generate a supercavity between each lateral side of said endplate andwater passing over said endplate, in use, at a zero yaw condition at adesign cruise speed with said endplate immersed in water to a designimmersion depth,

an aft portion terminating in a trailing edge, and

a protrusion on each opposing side of said front portion, at a lowerregion thereof and aft of said nose, for engaging water passing outsideof said supercavity, on the upstream side of said endplate when saidendplate is yawed with respect to said water passing over said endplateand/or on both sides of said endplate when said endplate is immersedbeyond said design immersion depth, each said protrusion extending in aspan-wise direction and having a face configured to create a stabilisingmoment upon engaging said water, said lower region having a length insaid span-wise direction at least equal to said design immersion depthof said endplate.

In yet another broad form the present invention provides a wing inground effect vehicle having a wing structure with opposing wing tipportions and a pair of supercavitating endplates each extendingdownwardly from a respective said wing tip portion to below saidfuselage and wing structure for immersion in water during flightthereover, each said endplate having:

a proximal root,

a distal tip,

a forward portion including a nose defining a leading edge and adaptedto generate a supercavity between each lateral side of said endplate andwater passing over said endplate, in use, at a zero yaw condition at adesign cruise speed with said endplate immersed in water to a designimmersion depth, and

an aft portion terminating in a trailing edge,

wherein, over the lowermost 1200 mm of said nose, said nose has anaverage width not greater than 0.006 times said chord length and anaverage depth, measured in a chordwise direction, of not greater than0.83 times said nose average width.

The nose of each said endplate may be in the general form of atriangular prism extending in a spanwise direction.

Preferably, said forward portion of each said endplate tapers towardssaid nose.

In the preferred embodiment, said nose of each said endplate issubstantially flat and lies in a plane substantially perpendicular tothe chord-wise direction of said endplate.

Preferably, the width of said nose of each said endplate satisfies thefollowing equation:

$\frac{g\; H\; L}{8.8\; V^{2}} \leq h \leq {10\left( \frac{g\; H\; L}{8.8\; V^{2}} \right)}$

wherein h=nose width, g=acceleration due to gravity, H=design immersiondepth of said endplate, L=chord length of endplate, V=vehicle designspeed.

Preferably, each said supercavity has a length less than 5 times saidchord length at substantially all span-wise locations within 50% of saiddesign immersion depth from said endplate tip.

Preferably, over the lowermost 1200 mm of said nose, said nose has anaverage width not greater than 0.006 times said chord length and anaverage depth, measured in a chordwise direction, of not greater than0.83 times said nose average width.

Each said endplate may be provided with a protrusion on each opposingside of said front portion, at a lower region thereof and aft of saidnose, for engaging water passing outside of said supercavity on theupstream side of said endplate when said endplate is yawed with respectto said water passing over said endplate and/or on both sides of saidendplate when said endplate is immersed beyond said design immersiondepth, each said protrusion extending in a span-wise direction andhaving a face configured to create a stabilising moment upon engagingsaid water, said lower region having a length in said span-wisedirection at least equal to said design immersion depth of saidendplate.

Each said protrusion may be in the form of a flap means configurablebetween a retracted position within said endplate and an extendedposition protruding beyond said endplate for engaging said water passingoutside of said cavity.

Alternatively, each said protrusion is fixed.

Preferably, each of said protrusions has a concave front surface facingsaid leading edge.

Each said endplate may be provided with a retractable leading edgedevice of greater width than said nose, said leading edge device beingextendable along and over said leading edge.

Preferably, said leading edge device of each said endplate has asubstantially flat front surface lying in a plane substantiallyperpendicular to said chord-wise direction of said endplate.

Preferably, each said endplate is curved inwards towards the centre ofsaid vehicle at said tip.

Preferably, each said endplate is tapered in thickness from said root tosaid tip.

Preferably, said trailing edge of each said endplate is tapered.

Each said endplate may be provided with a plurality of wedge-shapedmembers secured to a lower region of said aft portion thereof, saidlower region having a length in said span-wise direction at least equalto a design immersion depth of said endplate.

Said distal tip of each said endplate may be lower at said trailing edgethan at said leading edge when viewed in a chord-wise direction.

Each said endplate forward portion may be provided with a pair ofsupport struts on opposing sides of said endplate and each secured at afirst end thereof to the respective said wing and at a second endthereof to said endplate toward said tip.

Preferably, each said support strut first end is displaceable withrespect to the respective said wing towards the respective said endplateroot.

Preferably, said forward portion of each said endplate is provided withapertures, forward of said protrusions, extending through the thicknessthereof.

Said leading edge of each said endplate may be raked aft.

Said leading edge of each said endplate may be located forward of theleading edge of the respective said wing at said endplate root.

Each said endplate may be retractably mounted with respect to said wingtip portion to thereby enable raising of said endplate.

Preferably, each said endplate is mounted on the respective said wingtip portion by fastening means designed to detach at a predeterminedload.

Each said endplate may be mounted on the respective said wing tipportion by explosive bolts.

Alternatively, a lower portion of each said endplate may be configuredto detach from an upper portion of the respective said endplate uponimpact of a predetermined load on said lower portion.

The fuselage and wing structure may form a flying wing structure.

Said root of each said endplate may be located outboard of and adjacentto the respective said wingtip portion with a gap therebetween, furtherwherein a seal spans said gap between said endplate root and saidwingtip portion towards the upper surface of said wingtip portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred forms of the present invention will now be described by way ofexample with reference to the accompanying drawings, wherein:

FIG. 1( a) is a front elevation view of a prior art Russian OrlyonokWIG.

FIG. 1( b) is a side elevation view of the WIG of FIG. 1( a).

FIG. 1( c) is a plan view of the WIG of FIG. 1( a).

FIG. 2( a) is a side elevation view of an endplate of the WIG of FIG. 1(a).

FIG. 2( b) is a cross sectional plan view of the endplate of FIG. 2( a).

FIG. 3( a) is a side elevation view of a prior art endplate according tothe Barkley Report.

FIG. 3( b) is a cross sectional plan view of the endplate of FIG. 3( a).

FIG. 3( c) is an enlarged fragmentary cross sectional plan view of theendplate of FIG. 3( a).

FIG. 4( a) is a front elevation view of a prior art endplate accordingto Model No. 4 of the Barkley Report.

FIG. 4( b) is an inverse plan view of the endplate of FIG. 4( a).

FIG. 4( c) is a side elevation view of the endplate of FIG. 4( a).

FIG. 5( a) is a front elevation view of a prior art endplate accordingto the Moore Report.

FIG. 5( b) is an inverse plan view of the endplate of FIG. 5( a).

FIG. 5( c) is a side elevation view of the endplate of FIG. 5( a).

FIG. 6( a) is a front elevation view of a WIG according to a preferredembodiment of the present invention.

FIG. 6( b) is a side elevation view of the WIG of FIG. 6( a).

FIG. 6( c) is a plan view of the WIG of FIG. 6( a).

FIG. 7( a) is a cross sectional plan view of an endplate of the WIG ofFIG. 6( a).

FIG. 7( b) is a fragmentary front elevation view of the endplate of FIG.7( a) and adjacent wing structure.

FIG. 7( c) is a side elevation view of the endplate and wing structureof FIG. 7( b).

FIG. 7( d) is a fragmentary cross sectional plan view of the aft portionof the endplate of FIG. 7( a).

FIG. 8 is an enlarged fragmentary cross sectional plan view of theendplate of FIG. 7( a).

FIG. 9 is a fragmentary cross sectional plan view of a flat nosedendplate depicting drag forces in a yaw condition.

FIG. 10 is a fragmentary cross sectional plan view of a round nosedendplate depicting drag forces in a yaw condition.

FIG. 11 is a graph depicting drag versus speed for fully wetted andsupercavitating endplates.

FIG. 12( a) is a fragmentary front elevation view of an endplateaccording to a preferred embodiment of the present invention.

FIG. 12( b) is a cross sectional plan view of the endplate of FIG. 12(a) taken at section AA.

FIG. 12( c) is a cross sectional plan view of the endplate of FIG. 12(a) taken at section BB.

FIG. 12( d) is a cross sectional plan view of the endplate of FIG. 12(a) taken at section CC.

FIG. 12( e) is a fragmentary cross sectional plan view of the forwardportion of various endplates.

FIG. 13 is a schematic plan view of a flexed endplate.

FIG. 14 is a cross sectional plan view of the endplate of FIG. 12( a)generating a leading edge cavity.

FIG. 15( a) is a fragmentary front elevation view of an endplate andadjacent wing structure with support struts.

FIG. 15( b) is a side elevation view of the endplate of FIG. 15( a).

FIG. 16( a) is a side elevation view of an endplate with a leading edgedevice.

FIG. 16( b) is a fragmentary cross sectional plan view of the endplateof FIG. 16( a).

FIG. 17( a) is a fragmentary cross sectional plan view of an endplatewith flaps.

FIG. 17( b) is a side elevation view of the endplate of FIG. 17( a).

FIG. 18( a) is a fragmentary cross sectional plan view of an endplatewith a fixed protrusion.

FIG. 18( b) is a side elevation view of the endplate of FIG. 18( a).

FIG. 19( a) is a cross sectional front elevation view of an endplatesupport structure, taken at a section immediately forward of the pivotaxis.

FIG. 19( b) is a fragmentary cross sectional front elevation view of thestructure of 19(a) taken at a section aft of the pivot axis.

FIG. 19( c) is a cross sectional side elevation view of part of thestructure of FIG. 19( b).

FIG. 20( a) is a plan view of a flying wing according to a preferredembodiment of the present invention.

FIG. 20( b) is a front elevation view of the flying wing of FIG. 20( a).

FIG. 20( c) is a side elevation view of the flying wing of FIG. 20( a).

FIG. 21( a) is a front elevation view of an alternate flying wing.

FIG. 21( b) is a side elevation view of the flying wing of FIG. 21( a).

FIG. 22 is an enlarged fragmentary cross sectional plan view of a noseof an alternate endplate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 6( a) through 6(c) depict a wing in ground effect vehicleaccording to a preferred embodiment of the present invention. The wingin ground effect vehicle is provided with a fuselage 2 and wingstructure 3 with opposing wing tip portions. A pair of endplates 17,each having a proximal root 33, bottom or distal tip 19, leading edge 20and trailing edge 22, extend downwardly from endplate bulkheads 34 atthe wingtip portions to below the fuselage 2 and wing structure 3. Thisenables the endplates 17 to be immersed in water 26 during flightthereover as depicted in FIG. 6( b) whilst keeping the fuselage 2 andwing structure 3 airborne. In flight, the endplates will typically beslightly submerged below the surface 9 of the water 26 even in thetrough 18 of waves 21, depicted in phantom in FIG. 6( b). As there is noair gap between the distal tip 19 of the endplates 17 and the water 26the induced drag of the WIG is reduced, thereby increasing the lift/dragratio of the WIG. To maintain the endplates immersed in this mannerrequires the leading edge 20 of the endplates 17 to penetrate the waves21 to the height of the waves 21. With prior art endplates this wouldincur unacceptably high drag and/or divergence problems.

An endplate 17 according to the preferred embodiment is depicted inplan, front elevation and side views in FIGS. 7( a) though 7(c). Theforward portion 30 of the endplate includes a nose 28 defining theleading edge 20 of the endplate. The nose 28 is configured to generatean air-filled cavity 25 between each lateral side of the endplate andwater 26 which passes over the endplate 17 in use when immersed. Thiscavity 25 is open to the surface of the water, and is accordinglyventilated by air from above the water surface 9. The nose 28 isconfigured such that it is supercavitating when at a zero yaw condition(zero yaw with respect to water flow) at the design cruise speed withthe endplate immersed in water to the design immersion depth. Asupercavity 25 is thus generated, being a cavity formed extending aftover the length of, and thereby encapsulating, the endplate. As there isno contact between the sides of the endplate and water 26 outside of thecavity, there are no frictional drag forces or divergent side forcesbetween the water 26 and the endplate 17. In the context of thisspecification, a cavity extending over substantially the entire lengthof the endplate, but wetting the trailing edge still defines asupercavity.

The profile drag of a supercavitating endplate 17 is proportional to thesize of the cavity 25. To minimise the profile drag the endplate 17should accordingly be designed such that the cavity 25 is not muchlarger than the endplate 17. A problem then arises that when theendplate 17 experiences a significant angle of yaw, the aft portion 27of the cavity 25 will move to one side so that the water 26 impacts onthe aft portion 23 of the endplate 17. This will produce a large sideforce on the upstream side of the endplate, resulting in the endplateneeding to be designed with sufficient structural strength to sustainthese forces. This results in excessively thick and rigid endplatestructures such as those of the prior art. The structural requirementfor thick endplates results in large drag forces, such that no real dragreduction benefit is achieved.

Displacement of the aft portion 27 of the cavity 25 under yaw such thatthe water 26 outside of the cavity 25 impacts on the endplate also leadsto friction drag between the endplate 17 and the water 26. Theadditional drag incurred when the water 26 contacts the aft portion 23of the endplate increases with the side force on the endplate 17.

These problems are overcome in preferred embodiments of the presentinvention by configuring the endplate such that the trailing edge 22 ofthe endplate 17 is laterally displaceable with respect to the wing tipportion by water flowing over the endplate, while at least part of theforward portion of the endplate 17 is laterally fixed. This provides aweathercock effect, such that when the endplate tends to yaw, waterpassing over the endplate on the upstream side will impart a side forceon the endplate aft portion 23 where there is contact with the water 26outside of the cavity 25, displacing the trailing edge 22 of theendplate toward the center of the cavity 25, aligning the endplate aftportion 23 with the waterflow.

In the preferred embodiment of the present invention, the lateraldisplacement of the trailing edge 22 is provided by pivotably mountingthe endplate 17 about a pivot axis P extending in a span-wise directionof the endplate. The forward portion of the endplate is accordinglylaterally fixed at the pivot axis P, allowing the endplate to pivot inthe same manner as a weathervane.

The endplate pivot axis P should be located forward of the hydrodynamiccentre of pressure of the endplate at design conditions of design cruisespeed with the endplate immersed to a design depth, with the inflow atan angle of yaw. The most forward location of the centre of pressurewill occur when the speed is low enough to wet the entire endplate 17length, such that no cavity is generated. For this fully wettedcondition, the centre of pressure will generally always be further aftthan 0.25 times the endplate chord length aft of the endplate leadingedge 20 (particularly if the aft portion of the endplate is longer, andaccordingly more deeply immersed, than the forward portion of theendplate). Accordingly if the pivot axis is forward of this point, atsay 0.2 times the chord length aft of the leading edge, the endplate 17will weathervane at all speeds and will not be subjected to large sideloads due to yaw. If the endplate 17 is assumed to be rigid there willthus be no cause for divergence. The pivot axis P could alternatively belocated aft of the hydrodynamic centre of pressure for some flightconditions if rotation of the endplate about the pivot axis wereactively controlled by flight control actuators.

Rather than have the entire endplate 17 pivot about the pivot axis P, analternative solution would be to have the front portion of the endplate17 fixed and the aft portion pivotably mounted about the pivot axis P.

As an alternative to pivoting the aft portion of the endplate, or theentire endplate, the front portion of the endplate could be fixed withthe aft portion of the endplate laterally flexible and mounted to theendplate forward portion. If the endplate aft portion is flexible, thelower immersed region of the endplate aft portion is able to ‘give’somewhat, without needing to rotate the endplate 17 to the same degreeas if it was stiff, or without rotating the endplate at all. This‘giving’ tends to align the endplate aft portion with the waterflow,reducing the side force on the endplate and the resulting drag. Theflexed endplate 17 also uses its stored energy to realign itself whenthe angle of yaw is decreased. In embodiments where flexibility of theendplate aft portion is entirely relied on for relieving side force, itis preferred that at least the aft 75% of the endplate is flexible,leaving up to the forward 25% of the endplate fixed.

The increased water pressure at depth produces a narrower cavity 25 atgreater depths, which requires a thinner endplate. Tapering theendplates 17 from the root 33 to the tip 19 helps achieve the desiredflexibility of the aft portion of the endplate mentioned above. Theleading edge 20 of the endplate 17 can be vertical or raked aft(depicted in phantom as a raked leading edge 20A in FIG. 7( c)) to lowerthe spray angle and increase the stability of the leading edge.

There is a pressure differential between the laterally inward andoutward facing side surfaces of the endplates 17 caused by liftgenerated by the wing structure 3. It is thus preferred that theendplates are curved inwards toward the centre of the vehicle at theleading and trailing edges 20, 22 and at the endplate tip 19,particularly if the endplate aft portion is made flexible as describedabove. The endplates 17 are also tapered toward the leading and trailingedges 20, 22.

With a smooth sea and no wind the WIG is flown at a height so that theendplate tips 19 are slightly below the surface 9 of the water 26.Gravity causes the base of the cavity to rise from the leading edge 20to the trailing edge 22. The endplate tips 19 may be deeper at thetrailing edge 22 than the leading edge 20 to exacerbate this effect suchthat the lower region of the aft portion of the endplate is always morein contact with the water than the lower region of the forward portion.This moves the hydrodynamic centre of pressure further aft of the pivotaxis P so that the endplate 17 pivots and aligns itself to the waterflow.

As depicted in FIGS. 7( c) and 7(d), the endplates may be provided witha plurality of wedge-shaped members 32 secured to a lower region of theaft portion 23 of the endplate that is immersed when the endplate isimmersed to the design immersion depth. These wedges 32 assist theweathercock stabilising effect when the endplates 17 are subject toincreasing yaw angles, which may occur with increasing wind and waveaction. This causes the back part 27 of the cavity 25 to move from sideto side so that the water impacts on the wedges 32. These wedges 32direct the water away from the side of the endplate 17, maintaining thesupercavity. The sideways force on the wedges produced by this contactwith the water again pivots the endplates 17 around the pivot axis P (orflexes the aft portion in fixed endplate embodiments with a flexible aftportion), so that the endplate 17 aligns itself again with the waterflow and the centre of the cavity 25. Although the wedges 32 incur aprofile drag it has been found that the total drag is less than that fora smooth surface if the speed of the WIG is above 100 knots (51 m/s) foran immersion depth of 12′ (3660 mm). Because the wedges 32 incuradditional air drag compared to a smooth surface, it does not pay tocover the total surface of the endplates 17 with these wedges 32, butonly the lower region of the aft portion 23 where the water contact isincurred.

Utilising the above mechanisms to provide a weathercock stabilisingeffect, aligning at least the aft portion 23 of the endplates 17 withthe waterflow when subject to yaw, severe side forces, mechanicalfailure and the bulk of the water/endplate friction drag are eliminated.

The above passive weathercock type mechanisms are the preferredembodiments of the present invention. However, state of the art sensors,computers and hydraulics are capable of actively aligning the endplates17 with the water flow if required. As discussed above, this will beparticularly appropriate if the pivot axis is too far aft to provide apassive weathercock effect at some slower speeds.

Commercial WIGs of the basic designs shown in FIGS. 1( a) to 1(c) and6(a) to 6(c) have a design cruise speed greater than 150 knots (77 m/s).At these relatively high speeds there are numerous nose shapes that willproduce a supercavity 25 when the endplate is immersed to a design depth(typically from about 4 feet (1220 mm) and up to about to 13 feet (4000mm) for sea state 4), including concave, convex, wedge, semicircular,parabolic, elliptical, circular arc and many more. Any of these shapescan produce a supercavity but the preferred nose shape, as depicted inFIG. 8, is a flat nose 28 lying in a plane perpendicular to thechord-wise direction of the endplate.

With reference to FIG. 9, a flat nose 28 can be shown to behydrodynamically stable. When an endplate with a flat nose 28 is subjectto a yaw angle α, the hydrodynamic centre of pressure acting on the nosemoves towards the upstream side of the nose 28. The resultant drag forceD, which acts perpendicular to the flat surface of the nose 28, providesa stabilising negative twisting moment about the centre of gravity (CG)(and the pivot axis P for a pivoting endplate). This negative twistingmoment turns the nose of the endplate 17 towards the direction of theincoming water rather than away from it. This stabilising momentcomplements the stabilising weathercock effect discussed above. Evenwhen subjected to an angle of yaw, the waterflow detaches at the lateraledges 31 of the nose, generating the supercavity 25 at the nose edgesand leaving the sides of the endplate forward portion 30 unwetted. Thisensures that no side forces are exerted on the sides of the endplateforward portion 25, which would otherwise produce an unstable positivetwisting moment. The flat nose is accordingly hydrodynamically stableand not subject to divergence.

The stabilising negative twisting moment of the flat nose 28 can becompared with the destabilising positive twisting moment of asemicircular nose 15 as depicted in FIG. 10. With this configuration,the hydrodynamic centre of pressure again moves toward the upstream sideof the nose 15, but given the convex surface of the nose, the drag forceD acting perpendicular to the surface, coupled with a force generated bypressure acting on the wetted area of the nose on the upstream side,provides a resultant force R with an unstable positive moment about thecentre of gravity (CG). A wedge shaped nose or any other shaped nosethat is wetted on the side will also be unstable in the same way.

A flat nose is also easy and inexpensive to manufacture to the desiredshape. This is important as the nose 28 shape decides the cavity 25 sizewhich in turn determines the drag. If the cavity 25 is too large theprofile drag will be too large and if the cavity 25 is too small thewater 26 will contact the sides of the endplate 17, also causingexcessive drag. In service the nose 28 will receive regular minor damagefrom impacting with small objects. This damage can be repaired easily insitu by simply grinding the damaged area flat. A complicated nose shapewould require the removal and replacement of the damaged part.

The flat nose shape also minimises surface cavitation as the waterventilates cleanly when it leaves the square corner 31. In contrast aconvex shape would likely suffer from surface cavitation that would eataway and destroy the desired shape.

The drag of a supercavitating shape is proportional to the size of thecavity 25 it produces. Whilst a flat nose 28 produces a larger cavity 25than a streamlined nose of the same width, the desired cavity size canbe produced with a flat nose by reducing the width of the nose 28.Therefore there is no drag penalty through using a non-streamlined noseshape.

To minimise the drag of the endplate, the thickness of the flat nose 20should be selected so that the length of the supercavity 25 generated ata design cruise speed with the plate immersed to a design immersiondepth is slightly longer than the chord length of the endplate, suchthat the entire endplate will be unwetted without the supercavity beingexcessively large, which would result in a large profile drag. Asupercavity length of less than 5 times the chord length, and moreparticularly less than twice the chord length, over at least the lower50% of the immersed lower region of the endplate is preferred.

Tests were carried out on a model of the endplate according to thepreferred embodiment in a high-speed, variable-pressure, water channelwith the cavitation and Froude numbers properly scaled. The experimentaldata obtained enabled the development of empirical equations whichenable the selection of the nose width. Based on the experimental data,the ratio of cavity length to nose width can be expressed as:

$\begin{matrix}{\frac{l}{h} = \frac{20\; C_{d}}{\sigma}} & \left( \text{1a} \right)\end{matrix}$where:

$\sigma = \frac{\rho\; g\; H}{{1/2}\;\rho\; V^{2}}$

l=cavity length,

h=nose width,

g=acceleration due to gravity=32.2 ft/s² (9.81 m/s²),

H=endplate immersion depth,

V=vehicle speed

ρ=density of water, and

C_(d) is the classical drag coefficient for a ventilated,supercavitating flat plate normal to the flow, with:

$\begin{matrix}{C_{d} = {\frac{2\;\pi}{\pi + 4} = 0.88}} & \left( \text{1b} \right)\end{matrix}$

Equation (1a) is in large disagreement with the linearised result givenin the literature, such as in the report “The Shape of Cavities inSupercavitating Flow” (Proc. 11th Int. Cong. of Appl. Mech., 1964) by M.P. Tulin (hereinafter referred to as the Tulin Report), where l/h=(8/πor π/2)C_(d)/σ² depending on the model used in the derivation of theequations. The large difference is probably attributable to free surfaceand gravity effects.

Using the empirical equation (1a) for the cavity length behind a flatnose, the nose width required to completely unwet an endplate of chordlength L immersed to a depth Hat a speed V, is:

$\begin{matrix}{h = \frac{g\; H\; L}{10\; C_{d}V^{2}}} & (2)\end{matrix}$

For example, for the flat plate nose, C_(d)=0.88 and for H=12′ (3.7 m),L=60′ (18.3 m) and V=200 knots (103 m/s) equation (2) gives

h=0.02′ (6 mm)

Furthermore, equations (1a) and (1b) may be used to derive the followingequation to estimate the area of the plate that is wetted for any valueof h, H, L, and V.

$\begin{matrix}{{\frac{S_{W}}{H\; L} = {1 - {\frac{C}{H\; L}\left( {1 + {l_{n}\frac{H\; L}{C}}} \right)}}},{\frac{C}{L} \leq H}} & (3)\end{matrix}$where S_(w)=wetted area, and

$C = \frac{20\; C_{d}V^{2}h}{2\; g}$The drag (D) of the endplate may then be shown to be:

$\begin{matrix}{\frac{D}{2C_{f}H\; L\;{1/2}\;\rho\; V^{2}} \approx {\frac{S_{W}}{H\; L} + \frac{C_{d}h}{2\; C_{f}L}}} & (4)\end{matrix}$where C_(f)=skin friction coefficient.

FIG. 11 provides a comparison of the estimated total drag at varyingspeeds for a supercavitating flat nosed endplate according to theexample (h=0.02′, H=12′, L=60′) as compared to an equivalent fullywetted endplate. Again for the flat nose, C_(d)=0.88. The total drag forthe wetted plate is obtained from:D(fully wetted)=4C _(f) HL(½σV ²)  (5)

The experiments also revealed that the cavity maximum thickness occurredat approximately half the cavity length and could be estimated by thefollowing empirical equation.

$\begin{matrix}{\frac{t_{\max}}{h} = {{approx}.\frac{11}{\sigma^{1/3}}}} & (6)\end{matrix}$where t_(max) is the cavity maximum thickness.

The Tulin Report states that the cavity shape is approximatelyelliptical downstream from the body creating the cavity, with the cavitymaximum thickness again occurring at approximately half the cavitylength.

If the nose width is specified at any vertical location along its span,equations (1)–(6) determine the cavity length and maximum thickness atthat depth H.

In a preliminary design the endplate thickness may be chosen to be, say0.75 t_(max), so as to be well inside the cavity. Taking the cavity tobe elliptical its cross section is now determined. However its shapenear the nose must be adjusted for the well-known theoretical cavityshape behind a flat plate.

FIGS. 12( a) to 12(d) show the resulting design for a constant nose 28thickness of 0.02′ (6 mm). FIG. 12( a) depicts a front elevation view ofthe immersed bottom 12′ (3.7 m) of the endplate from the water surface9. FIGS. 12( b) to 12(d) provide cross sectional views taken at thewater surface 9 (Section A—A), midway between the water surface and theendplate tip (Section B—B) and at the endplate tip 19 (Section C—C). Themaximum thickness of the endplate at these three sections is 1.6′ (488mm), 1.25′ (381 mm) and 1.0′ (305 mm) respectively. These maximumthicknesses are 75% of the expected cavity 25 thickness generated by the0.02′ (6 mm) thick nose 28 at a speed of 250 knots (129 m/s). The cavity25 is depicted in phantom and can be seen to begin at the endplate flatnose 28 and extend beyond the trailing edge 22 of the endplate. Toreduce drag, the endplate 17 is faired toward the trailing edge 22 overa distance approximately 5 times the thickness of the endplate 17 at thepoint of tangency of the fairing.

As noted above, the design depicted in FIGS. 12( a) to 12(d) is based onselecting the endplate maximum thickness to be 0.75 t_(max) of thecavity. In some cases it may be necessary to reduce the thickness of theplate to achieve complete ventilation of the cavity. For a nosethickness of 0.02′ (6 mm), however, the endplate thickness probablycannot be made much thinner and still maintain its structural integrity.As described above the endplates 17 experience a side force because ofthe pressure differential between the air on the inside and the outsideof the endplates caused by the lift of the wing. Whilst the endplateforward portion 30 must be made very thin to fit inside the cavity, itmust be of sufficient lateral stiffness to resist the above mentionedside force. The endplate forward portion 30 might be made of solid steelor titanium for strength and stiffness. With the endplate forwardportion 30 being tapered, its thickness increases with the distance fromthe leading edge 28. With high pressure differentials caused by highwing loadings it may be appropriate to extend the endplate forwardportion 30 forward of the wing leading edge 11. This is so sufficientthickness and strength can be achieved at the point adjacent to the wingleading edge 11, where the pressure differential becomes significant.

In some situations it might be appropriate to increase the nosethickness with an associated drag penalty in order to provide astructurally sound and fully ventilated design. It should be noted thatthe drag of the 0.02′ (6 mm) nose is so much less than the drag of thedesigns in the Barkley and Moore Reports that the drag of a flat nosedesign will remain much lower than the Barkley and Moore designs even ifthe nose width is increased by five or even ten times. In fact, the nosewidth must be increased by 140 times to equal the drag of the Barkleyand Moore designs if operated at 12′ (3.7 mm) immersion depth and usingthe drag they report.

FIG. 12( e) depicts the forward end portion 30 of the endplate 17 of thepreferred embodiment design described above, with a flat nose 28generating a narrow cavity 25. The endplate 17 is overlaid with scaledversions of the forward portion of two prior art endplates according tothe Barkely and Moore Reports. Model 1 of the Barkley Report provides anendplate 14 with a rounded nose 15 and forward portion 16 which has athickness of 1% of the chord length. The Moore endplate 57 has a wedgenose 58 and 2.2% thick forward portion. The wedge nose of the 4% thickendplate proposed by the Barkley Report model No. 4 (not shown) isthicker again. In comparison, the forward portion 30 of the endplate 17has a thickness of approximately 0.1% of the endplate 17 chord lengthwhen measured at 1% of the endplate chord length aft of the leading edge28. This is an order of magnitude thinner than the prior art thinendplates which rely on thickness to achieve strength and stabilityrather than by being hydrodynamically stable.

As these prior art noses 15, 56, 58 and forward portions fit outside thesmall sized cavity 25 generated by the flat nose 28 of the preferredembodiment of the present invention, they require or would generateunworkably large cavities creating drag at least an order of magnitudelarger than the flat nosed endplate 17 which, for a 60′ (18 m) longendplate has a drag coefficient of about 0.00029 at a design cruisespeed of 250 knots (129 m/s) and a design immersion depth of 12′ (3600mm). This drag coefficient is based on the submerged area of theendplate.

Whilst there will be no cause for divergence with the above describedendplate embodiments of the present invention if the endplates (or atleast the forward portions thereof) are assumed to be rigid, theendplates will always exhibit some degree of flexibility. At slow speedswhere at least part of the endplate sides are wetted, excessiveflexibility of the endplate may cause a particular form of divergence.With reference to FIG. 13, the endplate 17 will tend to bend about thepivot axis P when subjected to a minute yaw angle α. Water pressureacting on the upstream side of any wetted area of the forward deflectedportion of the endplate will produce an unstable moment, tending tofurther deflect the forward portion of the endplate 17 and potentiallyresult in divergence. If the side forces acting on the yawed endplateproduce an adverse hydrodynamic moment per degree of yaw that is greaterthan the structural stiffness of the endplate per degree of yaw,divergence is possible.

FIG. 14 depicts an endplate cross section with a cavity 71 of lengthl_(c), generated by the nose at low speeds. The cavity 71 extends fromthe leading edge, with the flow reattaching downstream to leave theremainder of the sides of the endplate wetted. The approximate length ofthe cavity 71 is given by equations (1a) and (1b) above. Clearly, theleading edge cavity length will have a major effect on the tendency todiverge. For example, equations (1) and (2) may be used to show that forH=12′ (3.7 m) and h=0.02′ (6 mm), the cavity length l_(c) will be 12′(3.7 m) at a speed of 95 knots (49 m/s). Accordingly, for an endplatewhere the pivot axis P is located 12′ (3.7 m) aft of the endplateleading edge, the entire forward portion 30 forward of the pivot axis Pwill remain unwetted and there will be no adverse moment created,therefore divergence is not possible.

The magnitude of the moment (M) about a pivot axis P located 12′ (3.7 m)aft of the leading edge, per degree of yaw (α), is approximately:

$\begin{matrix}{\frac{M}{\alpha} \approx {\frac{\Delta\; P\;\frac{1}{2}\rho\; V^{2}}{\frac{1}{2}\rho\; V^{2}}\frac{\left( {12^{\prime} - l_{c}} \right)^{2}}{2}}} & (7)\end{matrix}$

where ΔP is the differential pressure applied to the wetted portion ofthe endplate forward of the pivot axis.

Equation (7) assumes that the mean value of ΔP across the wetted portionof the endplate has its centre of pressure at (12−l_(c))/2. It isfurther assumed that ΔP/½ ρV² is a constant and independent of thecavity length and if l_(c) is replaced by the value given by equations(1a) and (1b), equation (7) becomes:

$\begin{matrix}{\frac{M}{\alpha} \approx \frac{\left. {{{const}.\frac{1}{2}}\rho\;{V^{2}\left( {12 - {{\left( {17.76\; h} \right)/2}{gH}}} \right)}V^{2}} \right)^{2}}{2}} & (8)\end{matrix}$

The maximum value of M/α in equation (8) occurs for H=12′ (3.7 m) andfor h=0.02′ (6 mm) when:

$\begin{matrix}\begin{matrix}{V = {{7.7/\sqrt{h\;}}{knots}}} \\{= {54.3\mspace{11mu}{knots}\mspace{11mu}\left( {27.9\mspace{11mu}{m/s}} \right)}}\end{matrix} & (9)\end{matrix}$

This means that divergence is not likely to occur at speeds greater than54 knots, but may occur at speeds less than 54 knots. The likelihood ofdivergence is then dependent on the method of construction of theendplate.

If the front 30% of the endplate were constructed of a structurallyrigid material such as a titanium skin over a solid carbon matrixcentre, careful analysis would be required to determine if the endplatewould or would not diverge. This solid construction would however incura large weight penalty. To save weight, lighter weight construction isdesired, however such lighter weight constructions will be moreflexible, and hence divergence would be more likely in the lower speedranges.

One possible solution to this problem would be to increase the nose 28thickness and thus the total endplate 17 thickness so as to provide amore rigid structure. This has the disadvantage, however, of increasingthe drag, which is proportional to the nose thickness.

A preferred way of stiffening the forward portion 30 of the endplate isto support the endplate forward portion with a pair of support struts 59as depicted in FIGS. 15( a) and 15(b). The struts 59 are provided onopposing sides of the endplate 17 and are each secured at their upperfirst end to the wing 3, here at the wing tip portion, and at theirlower second end to the endplate 17 toward the tip 19. These struts 59would act in tension and would typically be configured to have some ofthe low drag features of the endplates 17, i.e. supercavitating,ventilating, non-divergent, flat nose, thin cross-section, tapered tofit inside the strut 59 cavity. The upper end of the struts are heredisplaceable with respect to the wing 3 toward the endplate root 33,such that at supercavitating speeds the struts 59 can be drawn up nextto the endplate 17, inside the endplate 17 cavity 25 for zero drag. Thistype of strut 59 can be used in any underwater situation where low dragat high speed is required.

The hydrodynamic moment about the pivot axis at a specific low speeddepends on the length of the cavity 25 generated at that speed. Forexample, if the cavity length extends to the pivot axis P, as per theexample above, there can be no adverse moment and no possibility ofdivergence. Consequently, it is possible to avoid divergence at any lowspeed if the nose 28 width could be temporarily increased to increasethe length of the cavity 25.

The required flat nose 28 thickness can be calculated as above and anyother method of diverting the water sideways from the leading edge 20 ofthe endplate 17, including the following will achieve the desiredincrease in cavity 25 size.

Referring to FIGS. 16( a) and 16(b), this temporary increased nose widthcan effectively be provided by a retractable leading edge device 62, ofgreater width that the endplate nose 28, which is extendable along andover the nose 28. This leading edge device, in the form of a thickernose 62, is made in segments joined together in a chain so that it canbe stored inside the wing tip portion and then lowered or raised by thetoothed wheel 63 which slides the segments of the nose 62 down and upthe outside of the regular nose 28. This system is, however, somewhatcomplex.

An alternative configuration is depicted in FIGS. 17( a) and 17(b) whereprotrusions in the form of flaps 60, configurable between a retractedposition within the endplate and an extended position protruding beyondthe endplate, are located on each opposing side of the endplate forwardportion 30 behind the nose 28. At low speeds, the flaps engage water asthe small cavity generated by the nose 28 tends to close, regenerating afurther, larger cavity behind the flaps 60 which act as a large nose. Itis preferred that the endplate forward portion 30 is provided withapertures 67 extending though the thickness thereof to reduce anydestabilising sideforce caused in yaw if the forward portion 30 in frontof the flaps is wetted. Here the forward portion 30 is formed ofhorizontal reinforcement plates 66 leaving large spaces 67 between theplates 66 for cross flow of water whilst maintaining lateral rigidity ofthe forward portion 30.

When the endplate is subject to yaw, even at supercavitating speeds, theflaps can be extended such that the flap 60 on the upstream side willengage water passing outside of the supercavity. The forward face of theflap 60 is flat and extends at right angles to the chord line of theendplate such that the pressure of the water impacting on the flap 60will create a stabilising moment. The flaps 60 extend in the spanwisedirection of the endplates and need only be provided in the lowerimmersed region of the endplates.

Flaps 60 will, however, potentially result in weakening of the endplateforward portion structure, and are mechanically complex.

In yaw a simple flap at or near the nose could be extended on one sidewhen the yaw condition is sensed to temporarily increase the cavitywidth and avoid that side of the endplate from wetting. During extensionof this flap, however, the resultant force acting on the flap, would actin front of the centre of gravity of the endplate resulting in a severedestabilising moment. At WIG speeds this would cause the endplate tofail unless it was made unduly thick resulting in a high drag. Thisalternative is therefore not suitable for a WIG.

A simpler solution is provision of a fixed protrusion 64 on each side ofthe endplate forward portion 30 as depicted in FIGS. 18( a) and 18(b),effectively providing a two-stage nose.

Experiments in a water channel demonstrated that the cavity size couldbe increased at slower speeds by this passive design which has theadditional advantage of increasing dynamic stability at increasingspeeds.

As explained above, for the example endplate dimensions, divergence ismost likely to occur at speeds less than 55 knots (28 m/s) because theleading edge cavities 25 a are too short to relieve the hydrodynamicmoment about the pivot axis P resulting from the wetted region forwardof the pivot point P. Experiments show that if a protrusion, or secondnose 64, whose total width is 0.25′ (76 mm) is located about 2.5′ (760mm) downstream of the 0.02′ (6 mm) wide nose 28, water will impact theprotrusion 64 and create a second, much longer, cavity 25 b that extendsto the pivot axis P (12′ aft of the leading edge) at about 20 knots (10m/s). Thus the possibility of divergence is eliminated at speeds greaterthan about 15 knots (8 m/s). As the speed is increased the leading edgecavity 25 length increases and finally at speeds greater than about 100knots (51 m/s) the leading edge cavity 25 completely clears and unwetsthe protrusion 64, thus eliminating the drag of the protrusion 64.

As per the embodiment of FIGS. 17( a) and 17(b), the endplate forwardportion forward of the protrusion 64 is provided with apertures 67extending through the thickness of the endplate, defined by horizontalreinforcement plates 66. This hollow space 67 allows the water to crossover from one side of the endplate to the other, thus avoiding sidewayspressure on the forward portion 30 of the endplate and thereby avoidingdivergence or failure in yaw. It also allows the water to come intocontact with the full face of the protrusion 64 to create the largercavity.

The front face of the protrusion is configured to be hydrodynamicallystable, here being concave in form. In yaw, the cavity will move to oneside and water on the upstream side of the endplate will impact on thefront face of the protrusion at the upstream side. The centre ofpressure applied by the water on the protrusion 64 will be on theupstream side of the endplate, and given that the front face is inclinedforward as opposed to swept back, the resultant load actingperpendicular to the concave face will create a stabilising moment aboutthe pivot axis (and centre of gravity) opposing any divergence. Aconcave protrusion 64 provides a significantly greater stabilisingmoment than would an equivalent flat protrusion once a reasonably largecavity has been formed.

A further advantage of this type of protrusion forming a second stagenose 64 is that it can be used to reduce the overall drag of theendplate 17. With a single stage nose 28, the nose width at the endplatetip 19 must be chosen to produce a large enough cavity 25 at the tip 19when immersed to the design maximum immersion depth. This nose width 28is approximately 6 times the appropriate width if it was only operatingat the mean average wave height. For instance in sea state 4 the highestwave is approximately 13.3′ (4050 mm) but the average wave height isonly 4.2′ (1280 mm). If the vehicle is flown such that the endplate tipremains just immersed at the trough of an average height wave, the meanimmersion depth will be 4.2′/2=2.1′ (640 mm).

The drag can therefore be reduced with a two stage nose by choosing asmaller nose thickness that would produce a sufficiently large cavity at2′ (610 mm) immersion depth and using the second stage nose toautomatically increase the cavity size at increased depths in the sameway that it automatically increases the cavity size at slower speeds. Asthe drag is proportional to the cavity size, this results in a loweraverage drag.

The structure used to pivotally mount the endplate 17, for pivotingembodiments, to the wingtip portion is depicted in FIGS. 19( a) to19(c), with further reference to FIG. 7( c). The pivotal mounting aboutthe pivot axis P is here provided by way of vertically aligned bearings35 that allow the endplate 17 to rotate horizontally while stillremaining vertical. The aft portion of the endplate is supported with astructure that allows the endplate 17 to rotate from side to side whilestill remaining vertical. The endplate mounting structure also enablesthe endplates to be raised if an object in the water is detected bysonar or equivalent so as to avoid damage. The endplates 17 can also beraised to reduce the draft of the WIG in port.

Horizontally configured bearings 36 are on the end of the struts 37, 38and the corners of the plate 44 and the box section 45. Verticalbearings 35, 43 allow the endplate 17 to rotate and align itself withthe water flow. The endplate 17 is raised by extending the hydraulicrams 39, 48, at the same time the hydraulic ram 40 is extended to keepthe endplate 17 vertical. The solid strut 41 maintains a constantdistance between two of the bearings 36A and 36B. The solid strut 42 isin the same vertical alignment as strut 41 but extends aft from thelower bearing 36A to bearing 36C (FIG. 7( c)). It thereby keeps theendplates from moving forwards or backwards.

The vertical alignment of the endplate 17 is achieved by the structureshown in FIG. 19( b). This structure joins the endplate bulkhead at thewingtip portion with the wing 3 at the fore and aft position shown in7(c). The plate 44 slides in and out between the roller bearings 46,which are between the plate 44 and the box section 45. Pressuredifferential on the endplate 17 forces the endplate to rotate on thebearing 36D outwards at the tip 19 and inwards at the top of thebulkhead 34 until the top part of the endplate bulkhead 34 comes incontact with a stop 49 on the top of the plate 44.

The flexible seal 50 prevents air escaping between the upper edge of theendplate bulkhead 34 and the wing 3. The seal is on the top of theendplate bulkhead 34 rather than the bottom so that the air pressureacting outwards on the endplate bulkhead 34 partially counteracts theturning moment of the air pressure acting on the endplate 17. Thisreduces the twisting moment on the endplate mounting structure.

When the endplates 17 are in the water 26 they can be used formaintaining the direction of travel and steering the WIG. The hydraulicram 47 moves the endplate 17 from side to side to alter the fore and aftalignment of the WIG. This same mechanism is used to control theendplate 17 alignment at slow subcavitating speeds as well as duringfree flight and PAR operations. The wing lift during these PARoperations is increased over the prior art because the elimination ofthe air gap 8 prevents pressurised air from escaping sideways.

The endplates 17 may also be attached to the wingtip portion by way offastening means, such as explosive bolts, designed to detach at apredetermined load, such as will occur when the endplate impacts a largeobject in the water. The endplates 17 will then separate from the WIGwithout causing any damage to the WIG.

Alternatively, the endplates 17 may be configured such that a lowerportion of the endplate detaches from the upper portion on impact, thusleaving the upper portion of the endplate to work, albeit inefficiently.

The endplate bulkhead at the wing tip portion is thicker than theendplate 17 and is contoured sideways and vertically for minimum airdrag. The additional thickness provides additional strength forspreading the loads from the attachment points 35, 43, to the rest ofthe endplate 17.

In another embodiment of the present invention, the WIG is configuredsuch that the fuselage and wing structure form a flying wing structurewithout a separate distinct fuselage. This embodiment, shown in FIGS.20( a) to 20(c) would theoretically be more efficient for larger WIG'sthan the seaplane configuration shown in FIGS. 6( a) to 6(c). Theendplates 52 have the same features as the endplates 17 used in the seaplane configuration and they eliminate the gap between the wing 51 andthe water 53 in the same way.

A flying-wing configuration eliminates the fuselage and tail therebyreducing the weight and skin friction. The disadvantage of a flying-wingis that it has a reduced internal volume. This disadvantage can beovercome by increasing the thickness of the wing in the alternateembodiment of FIGS. 21( a) and 21(b). The thicker wing 54 would requireboundary layer control to reduce separation and its associated drag toan acceptable level.

The combination of a thick wing 54 and surface piercing endplates allowsa high wing lift coefficient to be used without unduly increasing theinduced drag. This configuration has a very high lift/drag ratio.

Whilst the embodiments of the present invention described above allallowed for lateral displacement of the trailing edge of the endplate toprovide a weathercock stabilising effect, the applicant also envisagesforms of endplate which will not require the provision of a pivotalmounting of the endplate or equivalent to provide the weathercockeffect.

As described above, the WIG is typically flown with the endplatesconstantly in the water. This is contrary to the prior art and has theadvantage of creating a very large reduction in the yaw angle of theendplates. For instance, a WIG flying completely above the water surfaceat 150 knots (77 m/s) with a 40 knot (21 m/s) sidewind would have asideslip angle of approximately 15°. If however the endplates areconstantly in the water there is no sideslip angle created by the windand the only yaw angle is that created by the sideways orbital velocityof wave action. This water velocity at the surface is likely to be lessthan 5 knots (2.6 m/s) for a sea state 4 creating an endplate yaw angleof only approximately 2°. This angle will reduce further with increasingspeed of the WIG.

If an endplate nose shape is now chosen so that the cavity length atcruise speed is increased to several, say 5, times the endplate chordlength, there will also be a linear increase in the cavity width. Thisincreased cavity width, because of the reduced yaw angle, may now besufficient to accommodate the small yaw angles without the aft portionof the endplate wetting and creating additional side force and drag.With the cavity not moving laterally sufficiently to impact theendplate, the need to align the endplate aft portion with the incomingwaterflow is reduced.

As the cavity drag is proportional to its length, this endplate wouldhave a higher cavity drag than a pivotable endplate with a cavity lengthonly slightly longer than the endplate chord length. It would howeverhave the advantage of decreased complexity which is desirable.

To avoid the need to pivot the endplate, a nose should be designed whichis sufficiently narrow to provide low drag characteristics whilst stillgenerating a supercavity with a length several times the endplate chordlength at design cruise speeds so as to allow for small yaw angles. Thenose should also generate a sufficiently long cavity at low speeds suchthat adverse twisting moments about the endplate centre of gravity donot tend to excessively flex the endplate forward end portion of theendplate and cause divergence.

Whilst a suitable nose shape is a flat nose as discussed above inrelation to the above described embodiments of the present invention,other shapes will also be suitable and capable of generating thenecessary supercavity. A particular advantage of the flat nose is thatit creates a stabilising twisting moment about the pivot axis of apivoting endplate, and accordingly a stable twisting moment would alsobe created about the centre of gravity of a fixed endplate. The cavitygenerated by the flat nose 28 is created at the edge 31 of the flatnose, such that the entire forward end portion 30 of the endplate isunwetted.

Alternate nose designs, however, that have part of the forward endportion toward the leading edge wetted upstream of the waterflowdetachment point initiating the cavity, will also be acceptable, so longas the leading edge wetted length is sufficiently low to keep theresulting side forces, tending to laterally flex the endplate forwardportion in a divergent manner, to a manageable level at high cruisespeeds.

A suitable nose shape is a triangular prism resembling a simple broadwedge with a width of 0.006 times the chord length and a maximum depthin the chordwise direction of less than 0.83 times the nose width. Thisprovides a maximum nose depth of 0.005 times the chord length for amaximum width endplate. Such a nose configuration is depicted in FIG.22, where the nose 78 has two inclined faces 79. These maximumdimensions need only apply as an average over the lowermost 4 feet (1200mm) of the endplate, allowing operation at a design immersion depth of 4feet (1200 mm). For larger design immersion depths, these nose sizerestrictions should apply over a greater span of the endplate. The noseshould also be sufficiently wide to produce a supercavity at designcruise speeds. The wedge dimensions, and particularly the restriction onthe relative depth, will ensure a sufficiently blunt nose shape to keepany wetted length at the leading edge sufficiently low.

Other more streamlined shapes can be used provided the width and depthlimitations set out above are met. Curved nose faces are not preferred,however, because of the dangers of face cavitation at the high cruisespeed of WIGs. This cavitation may cause the problem of variable drag,resulting in a variable and unpredictable cavity size. To asses thestability of an endplate with a nose as described above, we cancalculate the minimum velocity required to produce a cavity extending toat least the mid chord point of the endplate which will be theapproximate location of the centre of gravity of the endplate. This willresult in there being no large wetted area forward of the centre ofgravity which could tend to adversely flex the endplate to causedivergence.

This velocity can be calculated by combining equations 1(a) and 1(b) toarrive at:

$V = \sqrt{\frac{lgH}{10\; h\; C_{D}}}$

where:

C_(D)=0.51=drag coefficient of a wedge with the above maximum dimensions(thickness/chord=1.2)

H=13.32′ (4060 mm)=Maximum wave height for sea state 4,

l=60′/2=30′ (9140 mm)

The above provides a velocity V of 83 fps=49 knots (25 m/s).

The described nose shape will therefore unwet the front half of theendplate at the slow speed of 49 knots (25 m/s). This speed is lowenough to avoid low speed divergence caused by the side force acting ona large wetted area in front of the centre of gravity of the endplate(located at 50% of chord).

This nose shape 78 has a low wetted length (measured in the chordwisedirection) of 0.005 times the chord length (as only the faces 79 of thewedge shaped nose will be wetted) and as such the endplate will notdiverge at high cruise speeds.

In addition this nose shape has a narrow width of 0.006 times the chordlength so that the overall cavity drag coefficient is only 0.006×0.51(width×drag coefficient of this shaped wedge)=0.003 which is an order ofmagnitude less than that quoted by the prior art.

A fixed non-pivoting endplate with this nose can therefore be a verysatisfactory endplate. This nose shape can also be used on pivotingendplates such as those described above.

As described above in relation to the embodiment of FIGS. 18( a) and18(b), a 2 stage nose can be used to expand the cavity and avoiddivergence in yaw with a pivoting endplate. It is also possible to use aprotrusion 64, forming a 2 stage nose, on a fixed endplate provided theangles of yaw are small, as will be the case with the endplatesconstantly in the water as discussed above. It is therefore possible toconstruct a low drag fixed endplate that will not diverge or fail in yawby using a protrusion 64 forming a 2 stage nose and running theendplates constantly in the water.

The front nose 28 can be of any suitable shape to produce a supercavityat design cruise speeds with the endplates immersed to a designimmersion depth, however for the same reasons as set out above, thepreferred shape is flat. A flat nose does not incur any side force andthis is particularly important when the endplate is fixed and verynarrow to reduce the cavity drag. The front nose 28 should be sized toprovide a supercavity just longer than the endplate chord length and theendplate therefore has the same low drag as the rotating endplate whenthe endplate is not yawed.

In yaw, the protrusion 64 forming the 2nd stage nose will incuradditional drag caused by the pressure of the water on the 2nd stagenose 64. The average drag on the 2nd stage nose 24 will however be smalland this type of endplate is therefore an attractive option when it iswished to avoid the complexity of pivoting endplates.

1. A wing in ground effect vehicle having a fuselage, a wing structurewith opposing wing tip portions and a pair of supercavitating endplates,each of said supercavitating endplates extending downwardly from arespective one of said wing tip portions below said fuselage and saidwing structure for immersion in water during overwater flight of thevehicle, each said endplate comprising: a proximal root; a distal tip; aforward portion including a nose defining a leading edge of saidendplate and terminating in a nose lateral edge on each lateral side ofsaid endplate, said nose being adapted to generate a cavity extendingrearwardly from each said nose lateral edge between a respective one ofsaid lateral sides of said endplate and water passing over saidendplate, in use, at a zero yaw condition at speeds up to and includinga design cruise speed with said endplate immersed in water to a designimmersion depth, said cavities forming a supercavity at said designcruise speed; an aft portion terminating in a trailing edge; and meanssupporting at least part of said forward portion of each said endplatelaterally fixed with respect to a respective one of said wing tipportions and supporting said trailing edge of each said endplatelaterally displaceable, with respect to a respective one of said wingtip portions, in response to water flowing over said endplate in use. 2.A wing in ground effect vehicle having a fuselage, a wing structure withopposing wing tip portions and a pair of supercavitating endplates, eachof said supercavitating endplates extending downwardly from a respectiveone of said wing tip portions to below said fuselage and said wingstructure for immersion in water during overwater flight of the vehicle,each said endplate comprising: a proximal root; a distal tip; a forwardportion including a nose defining a leading edge of said endplate andterminating in a nose lateral edge on each lateral side of saidendplate, said nose being adapted to generate a cavity extendingrearwardly from each said nose lateral edge between a respective one ofsaid lateral sides of said endplate and water passing over saidendplate, in use, at a zero yaw condition at speeds up to and includinga design cruise speed with said endplate immersed in water to a designimmersion depth, said cavities forming a supercavity at said designcruise speed; and an aft portion terminating in a trailing edge, saidnose of each said endplate being substantially flat and lying in a planethat is substantially perpendicular to a chord-wise direction of eachsaid end plate.
 3. The wing in ground effect vehicle according to claims1 or 2 wherein each said endplate is pivotably mounted about a pivotaxis, each said pivot axis extending in a span-wise direction of eachsaid endplate, said forward portion of each said end plate beinglaterally fixed at said pivot axis.
 4. The wing in ground effect vehicleof claim 3 further comprising means for actively controlling rotation ofeach said endplates about a respective one of said pivot axes.
 5. Thewing in ground effect vehicle according to claims 1 or 2 wherein saidforward portion of each said endplate is fixed, and said aft portion ofeach said endplate is pivotally mounted about a pivot axis, each saidpivot axis extending in a span-wise direction of said endplate.
 6. Thewing in ground effect vehicle of claim 3 wherein said pivot axis of eachsaid endplate is located forward of a hydrodynamic center of pressure ofsaid endplate at said design cruise speed with said endplate immersed inwater to said design immersion depth.
 7. The wing in ground effectvehicle of claim 5, wherein said pivot axis of each said endplate islocated forward of a hydrodynamic center of pressure of said endplate atsaid design cruise speed with said endplate immersed in water to saiddesign immersion depth.
 8. The wing in ground effect vehicle of claim 3,wherein said pivot axis of each said endplate is located less than 0.25times the chord length of said endplate aft of said leading edge at aspan-wise position midway between said endplate root and tip.
 9. Thewing in ground effect vehicle of claim 5, wherein said pivot axis ofeach said endplate is located less than 0.25 times the chord length ofsaid endplate aft of said leading edge at a span-wise position midwaybetween said endplate root and tip.
 10. The wing in ground effectvehicle according to claims 1 or 42 wherein said forward portion of eachsaid endplate is fixed, and said aft portion of each said endplate islaterally flexible and is mounted to said forward portion.
 11. The wingin ground effect vehicle of claim 10, wherein said aft portion of eachsaid endplate extends forward of a hydrodynamic center of pressure ofsaid endplate at said design cruise speed with said endplate immersed inwater to said design immersion depth.
 12. The wing in ground effectvehicle of claim 10, wherein said aft portion of each said endplate hasa chord length of at least 0.75 times the chord length of said end plateat a span-wise position midway between said end plate root and tip. 13.A wing in ground effect vehicle having a fuselage, a wing structure withopposing wing tip portions and a pair of supercavitating endplates, eachof said supercavitating endplates extending downwardly from a respectiveone of said wing tip portions below said fuselage and said wingstructure for immersion in water during overwater flight of the vehicle,each said endplate comprising: a proximal root; a distal tip; a forwardportion including a nose defining a leading edge and adapted to generatea supercavity between each lateral side of said endplate and waterpassing over said endplate, in use, at a zero yaw condition at a designcruise speed with said endplate immersed in water to a design immersiondepth; an aft portion terminating in a trailing edge; and a protrusionon each opposing side of said front portion, at a lower region thereofand aft of said nose, for engaging water passing outside of saidsupercavity, on the upstream side of said endplate when said endplate isyawed with respect to the water passing over said endplate and/or onboth sides of said endplate when said endplate is immersed beyond saiddesign immersion depth, each said protrusion extending in a span-wisedirection and having a face configured to create a stabilizing momentupon engaging the water, said lower region having a length in saidspan-wise direction at least equal to said design immersion depth ofsaid endplate.
 14. A wing in ground effect vehicle having a wingstructure with opposing wing tip portions and a pair of supercavitatingendplates each extending downwardly from a respective one of said wingtip portions below said wing structure for immersion in water duringoverwater flight of the vehicle, each said endplate comprising: aproximal root; a distal tip; a forward portion including a nose defininga leading edge and adapted to generate a supercavity between eachlateral side of said endplate and water passing over said endplate, inuse, at a zero yaw condition at a design cruise speed with said endplateimmersed in water to a design immersion depth; and an aft portionterminating in a trailing edge, said nose having an average width, overa lowermost 1200 mm of said nose, not greater than 0.006 times a chordlength of said endplate from said nose to said tip, and an averagedepth, measured in a chordwise direction, of not greater than 0.83 timessaid nose average width.
 15. The wing in ground effect vehicle of claim14 wherein said nose of each said endplate is in the general form of atriangular prism extending in a spanwise direction.
 16. The wing inground effect vehicle as in any one of claims 1, 2, 13 and 14, whereinsaid forward portion of each said endplate tapers towards said nose. 17.The wing in ground effect vehicle as in any one of claims 1, 13 and 14,wherein said nose of each said endplate is substantially flat and liesin a plane substantially perpendicular to the chord-wise direction ofsaid endplate.
 18. The wing in ground effect vehicle of claim 2, whereinthe width of said nose of each said endplate satisfies the followingequation:$\frac{g\; H\; L}{8.8\; V^{2}} \leq h \leq {10\left( \frac{g\; H\; L}{8.8\; V^{2}} \right)}$wherein h=nose width, g=acceleration due to gravity, H=design immersiondepth of said endplate, L=chord length of endplate, V=vehicle designspeed.
 19. The wing in ground effect vehicle of claim 17, wherein thewidth of said nose of each said endplate satisfies the followingequation:$\frac{g\; H\; L}{8.8\; V^{2}} \leq h \leq {10\left( \frac{g\; H\; L}{8.8\; V^{2}} \right)}$wherein h=nose width, g=acceleration due to gravity, H=design immersiondepth of said endplate, L=chord length of endplate, V=vehicle designspeed.
 20. The wing in ground effect vehicle as in any one of claims 1,2, 13 and 14, wherein each said supercavity has a length less than 5times said chord length at substantially all span-wise locations within50% of said design immersion depth from said endplate tip.
 21. The wingin ground effect vehicle as in any one of claims 1, 2 and 13 whereinover the lowermost 1200 mm of said nose, said nose has an average widthnot greater than 0.006 times said chord length and an average depth,measured in a chordwise direction, of not greater than 0.83 times saidnose average width.
 22. The wing in ground effect vehicle according toclaims 1 or 2 wherein each said endplate is provided with at least oneprotrusion on each opposing side of said front portion of said endplateand at a lower region thereof, and aft of said nose, said at least oneprotrusion engaging water passing outside of said supercavity on theupstream side of said endplate when said endplate is yawed with respectto said water passing over said endplate and/or on both sides of saidendplate when said endplate is immersed beyond said design immersiondepth, each of said protrusions extending in a span-wise direction andhaving a face configured to create a stabilizing moment upon engagingsaid water, said lower region having a length in said span-wisedirection at least equal to said design immersion depth of saidendplate.
 23. The wing in ground effect vehicle of claim 13 wherein eachsaid protrusion is in the form of a flap configurable between a retracedposition within said endplate and an extended position protruding beyondsaid endplate for engaging water passing outside of said cavity.
 24. Thewing in ground effect vehicle of claim 22 wherein each said protrusionis in the form of a flap configurable between a retracted positionwithin said endplate and an extended position protruding beyond saidendplate for engaging water passing outside of said cavity.
 25. The wingin ground effect vehicle of claim 13 wherein each said protrusion isfixed.
 26. The wing in ground effect vehicle of claim 22 wherein eachsaid protrusion is fixed.
 27. The wing in ground effect vehicle of claim13, wherein each of said protrusions has a concave front surface facingsaid leading edge.
 28. The wing in ground effect vehicle of claim 22,wherein each of said protrusions has a concave front surface facing saidleading edge.
 29. The wing in ground effect vehicle as in any one ofclaims 1, 2, 13 and 14, wherein each said endplate is provided with aretractable leading edge device of greater width than said nose, saidleading edge device being extendable along and over said leading edge.30. The wing in ground effect vehicle of claims 29 wherein said leadingedge device of each said endplate has a substantially flat front surfacelying in a plane substantially perpendicular to said chord-wisedirection of said end plate.
 31. The wing in ground effect vehicle as inany one of claims 1, 2, 13 and 14, wherein each said endplate is curvedinwards towards the center of said vehicle at said leading and trailingedges and at said tip.
 32. The wing in ground effect as in any one ofclaims 1, 2, 13 and 14, wherein each said endplate is tapered inthickness from said root to said tip.
 33. The wing in ground effectvehicle as in any one of claims 1, 2, 13 and 14, wherein said trailingedge of each said end plate is tapered.
 34. The wing in ground effectvehicle as in any one of claims 1, 2, 13 and 14, wherein each saidendplate is provided with a plurality of wedge-shaped members secured toa lower region of said aft portion thereof, said lower region having alength in said span-wise direction at least equal to a design immersiondepth of said endplate.
 35. The wing in ground effect vehicle as in anyone of claims 1, 2, 13 and 14, wherein said distal tip of each saidendplate is lower at said trailing edge than at said leading edge whenviewed in a chord-wise direction.
 36. The wing in ground effect vehicleas in any one of claims 1, 2, 13 and 14, wherein each said endplateforward portion is provided with a pair of support struts on opposingsides of said endplate, each of said support struts having a first endsecured to said wing and a second end secured to said endplate towardsaid tip.
 37. The wing in ground effect vehicle of claim 36 wherein eachsaid support strut first end is displaceable with respect to said wingtowards said endplate root.
 38. The wing in ground effect vehicle ofclaim 13, wherein said forward portion of each said endplate is providedwith apertures, forward of said protrusions, said apertures extendingthrough the thickness of said endplate.
 39. The wing in ground effectvehicle of claim 23, wherein said forward portion of each said endplateis provided with apertures, forward of said protrusions, said aperturesextending through the thickness of said endplate.
 40. The wing in groundeffect vehicle of claim 24, wherein said forward portion of each saidendplate is provided with apertures, forward of said protrusions, saidapertures extending through the thickness of said endplate.
 41. The wingin ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein said leading edge of each said endplate is raked aft.
 42. Thewing in ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein said leading edge of each said endplate is located forward of aleading edge of said wing at said endplate proximal root.
 43. The wingin ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein each said endplate is retractably mounted with respect to saidwing tip portion to thereby enable raising of said endplate.
 44. Thewing in ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein each said endplate is mounted on said wing tip portion byfastening means adapted to detach at a predetermined load.
 45. The wingin ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein each said endplate is mounted on said wing tip portion byexplosive bolts.
 46. The wing in ground effect vehicle as in any one ofclaims 1, 2, 13 and 14 wherein a lower portion of each said endplate isconfigured to detach from an upper portion of said endplate upon impactof a predetermined load on said lower portion.
 47. The wing in groundeffect vehicle as in any one of claims 1, 2, 13 and 14, wherein saidfuselage and said wing structure form a flying wing structure.
 48. Thewing in ground effect vehicle as in any one of claims 1, 2, 13 and 14,wherein said proximal root of each said endplate is located outboard ofand adjacent to said respective wingtip portion with a gap therebetween,and further including a seal spanning a gap between said endplateproximal root and said wingtip portion towards an upper surface of saidwingtip portion.